I know the fuel energy constant needs to be set to .680 when switching to E85 on my xfi --but what about the first time fuel is switched and there is still lets say 1.0 gallon of gas left in the tank after draining tank from the fuel rail and i add 10 gallons of e-85 would that make the fuel E-75 and should i set the fuel energy constant to about .725 to compensate ? or just leave it set to .680 and the xfi will compensate what ever the fuel is e-75 or e-80 e-83 or what ever it ma bee.....?.. I do not have the flex fuel sensor. thanks in advance.....